Experimental Pfizer breast cancer drug designated a 'breakthrough'

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TRENTON, N.J. -- Pfizer Inc. said Wednesday that its experimental pill for advanced, often deadly breast cancer has been designated as a breakthrough therapy by the Food and Drug Administration.

Pfizer shares jumped nearly 3 per cent following the news.

The breakthrough designation, created under legislation enacted last summer to fund and improve operations of the FDA, is meant to speed up development and review of experimental treatments that are seen as big advances over existing therapies for serious diseases. Pfizer is working with the agency to determine exactly what research results it will need to apply for approval of the drug.

Palbociclib is being evaluated as an initial treatment for the biggest subgroup of postmenopausal women whose breast cancer is locally advanced or has spread elsewhere in the body. About 60 per cent of women with such advanced breast cancer have tumors classified as ER+, or estrogen-receptor positive, but HER2-, or lacking an excess of the growth-promoting protein HER2.

Estrogen-receptor positive tumors have proteins inside and on the surface of their cells to which the estrogen hormone can attach and then fuel growth of cells. These tumors tend to grow slowly and can be fought with drugs that block estrogen's effects.

Meanwhile, about 80 per cent of breast cancer tumour cells are HER2 negative. That means that unlike HER2 positive tumors, they don't produce too much of the HER2 protein, which makes tumors grow and spread more aggressively than in other breast cancer types.

New York-based Pfizer is currently running a late-stage study of palbociclib at multiple centres, comparing its effects when used in combination with letrozole with the effects of letrozole alone.

Letrozole, sold under the brand name Femara for about the past 15 years, is a pill that works by inhibiting aromatase. That's an enzyme in the adrenal glands that makes estrogen.

According to Pfizer, palbociclib targets enzymes called cyclin dependent kinases 4 and 6. By inhibiting those enzymes, the drug has been shown in laboratory studies to block cell growth and suppress copying of the DNA of the cancer cells.

Pfizer, which has made research on cancer medicines a priority in recent years, also is testing palbociclib as a treatment for other cancers.

In afternoon trading, Pfizer shares were up 83 cents, or 2.9 per cent, at $29.94.